1. Field of the Invention
The present invention relates to a fuel injection control apparatus.
2. Description of the Related Art
FIG. 4 is a timing chart showing fuel injection states in a fuel injectable range of a four-cycle engine. When an engine starts, a rotation speed of the engine dramatically changes. Thus, when a necessary fuel injection amount (period B-D) is supplied in a fuel injection valve, there is a large difference between engine rotation speed at the time of computing the necessary fuel injection amount and engine rotation speed at the time of actually supplying the fuel. It is difficult to control both a fuel injection start timing (B) and a fuel injection finish timing (D). Also, it is difficult to have the fuel injection finish timing (D) fixed and have the fuel injection start timing (B) variable.
For example, Japanese Unexamined Patent Application, First Publication No. H9-242586 discloses a technique that a fuel injection start timing (injection start timing at starting) at the engine starting can be previously set and at the time of engine starting, fuel is injected only for the injection period corresponding to the rotation number of the engine in which the injection starting timing at the engine starting is a starting point (in other words, the injection start timing is fixed and the injection finish timing is variable).
However, in the case that fuel is alcohol or the like, when a necessary fuel injection amount is largely increased (period B-F), fuel which is not injected (period E-F) over a final end (E: for example, finish timing of the intake stroke) of the fuel injectable range is generated. In order to avoid this, a large capacity fuel injection valve needs to be used so that the injection timing is not over the final end (E) of the fuel injectable range for any necessary fuel injection amount.
However, to satisfy the above-described condition and to be applicable to both gasoline fuel and alcohol fuel, the fuel injection valve having a flow capacity 1.5 times of that needed in the case of gasoline fuel may be used. In this case, there is a problem that controllability becomes worse in terms of the control when gasoline fuel is used. On the other hand, in the case that the fuel injection start timing (B) is advanced to timing A in FIG. 4 to correspond to alcohol fuel in which the necessary fuel injection amount is large, the alcohol fuel can be injected within the fuel injectable range (period A-E). In the case that gasoline fuel in which the necessary fuel injection amount is small, fuel cannot be injected during the intake stroke (period A-C). Thus, there is a problem that performance of the engine worsens.
In view of the aspects described above, an object of the present invention is to provide a fuel injection control apparatus in which the fuel injection can be performed at an appropriate timing irrespective of the necessary fuel injection amount.